The objective of the proposed research is to further understanding of the molecular mechanism which insures the accurate segregation of the unit-copy P1 plasmid to daughter cells during cell division. The processes which lead to the equitable distribution of chromosomes during mitosis and the forces which disrupt the process in neoplastic cells are not well understood on a molecular level. In order to have a simple model system for this process it is important to address this problem in bacteria which has both powerful genetic tools and unique genetic elements which serve as model chromosomes. The experimental design centers on genetic schemes for identifying the components and structures involved in the process and on direct tests of aspects of relevant models for how partition works. Both strategies are designed to create a comprehensive understanding of the mechanism of partition and how it is integrated in the cell cycle.